1. Field of the Invention
The present invention relates to the control of hydraulic actuators, and more particularly to controlling the speed of a hydraulic motor under varying load conditions.
2. Description of the Related Art
Some hydraulic motors have inherently low damping which makes accurate speed control difficult under varying load conditions. As a result, the device being moved by the motor may overshoot or undershoot a desired position or operate at too great a velocity if velocity is the controlled attribute.
For example, hydraulic motors are used to open and close the weapons bay doors on military aircraft. If the door does not open fully because of an unexpectedly large load acting of the motor, such as a high speed wind, the weapons may not fully deploy. Conversely if the load is unexpectedly small and the motor operates longer than necessary, the door will be forced against a mechanical stop which can damage the door or the motor. In addition to changing load conditions, other factors, such as variation of hydraulic fluid flow to the motor, also affect the speed of the motor. Thus, if the motor is operated based on an assumed speed and the actual speed is different, the member being moved may not be properly positioned.
Therefore, it is desirable to provide a mechanism to determine when various factors cause variation in motor speed and compensate for that variation.